During pyrolysis, or dry distillation, organic input material is heated without the presence of oxygen whereby the material is not combusted but instead is converted to simpler components in the form of fluid and gaseous products that are recovered through a sequence of subsequent process stages that includes condensation. The said pyrolysis technology is normally used for the recovery of the fuel, such as rubber material, that is present in, for example, discarded tyres or in various types of plastic material. During complete pyrolysis, known as “carbonisation”, the residue or remainder consists entirely of carbon.
The input material is fragmented during the pyrolysis process to fragments of suitable size, washed, and pre-heated to approximately 100-150° C., after which the material is inserted or loaded into a reactor, known as a “retort”, that has the form of a furnace, for conversion to gas, which normally takes place at temperatures of around 450-700° C. A volatile gas, known as “pyrolysis gas”, is obtained from the pyrolysis process, which gas contains, in addition to water vapour, carbon monoxide, carbon dioxide, paraffins, olefins, and a number of further hydrocarbons from which oil and gas can be recovered. Carbon black or active carbon can be produced from the solid carbon-containing residue in the reactor after the pyrolysis process. If the residue or coke that remains after the pyrolysis process is to be used as solid fuel, it is separated by sieving from undesired substances such as, for example, steel or glass fibre residue. In the case in which the coke is to be further refined to carbon black or active carbon, further stages of pyrolysis treatment must be carried out, in steps that comprise, among other steps, a raising of the temperature to between 800-900° C. in order to remove any traces of volatile hydrocarbons, a subsequent lowering of the temperature, and possibly steam treatment.
The pyrolysis products that are obtained are very valuable as industrial raw materials, and they normally have qualities that are fully comparable to those of raw materials produced in a conventional manner.
Experiments have shown that the properties and the quality of the said products that have been produced by pyrolysis are determined to a large extent as early as the pyrolysis process, and determined by how well the operating conditions and parameters with respect to, for example, temperatures, rates of heating, retention times, and the concluding cooling times in the reactor can be controlled and monitored during the pyrolysis process.
Reactors are known that allow the return or recirculation of the pyrolysis gas that is formed through the reactor. in order to be able to control and regulate the pyrolysis process more accurately. Such a reactor is known from, for example, SE 513 063 and it is described as a reactor consisting of a chamber that can be opened, which in its closed condition is sealed from the surrounding atmosphere. The chamber is provided with an inlet at one end and an outlet at a second end such that inert or inactive gas at a freely chosen temperature can be circulated through the material that has been placed in the chamber. The gas is caused to pass axially through the chamber of the reactor and to move along its axial direction from the bottom upwards. Charging and emptying of the reactor takes place in batches with the aid of containers that can be exchanged and are provided with holes or perforations, which containers are lifted up and down in the reactor, whereby the gas is caused to pass through the said containers. The outlet is placed in connection with a condenser for the condensation of the pyrolysis gas that has formed to fluid-phase products, and the outlet has a circuit for recirculation of a fraction of the pyrolysis gas to the inlet. At the outlet are arranged not only a temperature detection means for the measurement of the temperature of the outgoing pyrolysis gas and thus for the regulation of the temperature of the gas that is led into the reactor through the inlet such that the temperature that has been determined in advance is maintained in the reactor, but also an arrangement that comprises sensor means, with the aid of which the various components of the pyrolysis gas and their relative amounts can be measured and analysed, whereby the process is maintained and allowed to proceed as long as the material in the reactor continues to emit pyrolysis gas. The said two measurement means are used in a manner based on feedback for the regulation of the operating conditions of the reactor and of its operating parameters.
Although the known reactors described above have proved to function well, they suffer from the disadvantage that the operating conditions inside the reactor itself cannot be controlled in a satisfactory manner. To be more precise, known reactors lack the possibility of being able to control and regulate in an efficient manner and inside the actual reactor chamber the direction of movement of the gas, its speed, its rate of flow and its temperature, during the pyrolysis process. The use of containers provided with holes or perforated that are placed into the reactor for its charging and emptying also influences in a negative manner the possibilities of controlling and monitoring the process parameters inside the reactor chamber.
Thus, a desire has existed for a long time to achieve a reactor with improved possibilities of controlling and monitoring the operating conditions and parameters in the reactor chamber during the pyrolysis process, and a first aim of the present invention is thus to achieve a reactor that makes this possible. A second aim of the invention is to achieve a reactor that allows improved flow of the heat-bearing gas through the reactor, even in cases in which the input material has a fragment size that is relatively low.
Known reactors can usually be opened at the bottom through a hatch arranged in the lower end-wall section of the reactor vessel, for emptying of the carbonaceous residue that remains in the bottom of the reactor chamber after the pyrolysis has been carried out. A defined hatch is not present in certain cases, and the reactor instead can be divided at the connection between the outer jacket and the lower end-wall section, whereby it is possible to access the residue for its removal or emptying of the divided reactor. Alternatively, emptying may take place in the manner described above, namely with the aid of perforated containers or containers provided with holes that are placed into and removed from the reactor chamber in a batchwise manner, through the hatch that is arranged in the upper end-wall section of the reactor vessel.
It should be understood that the requirement that it is to be possible to empty the reactor vessel through its lower end-wall section or at its bottom opposes the possibilities of being able to design the chamber that is a component of the reactor in a free manner, such that the possibilities of control and monitoring of the operating condition are optimised. The possibility of designing the reactor chamber with a fixed bottom that cannot be opened contributes to the ability to optimise the operating conditions without the need to consider the need that it must be possible to empty the reactor in a conventional manner, through, for example, a hatch in the bottom of the chamber. A third aim of the invention, therefore, is to provide a method that facilitates charging and emptying of a reactor of the present type, with a fixed bottom that cannot be opened, and which method has its special area of application for the pyrolysis treatment of input material with a relatively small fragment size.
Further characteristics and advantages of the invention are made clear by the dependent claims.